EP1318968A1

EP1318968A1 - Method for treating waste by hydrothermal oxidation

Info

Publication number: EP1318968A1
Application number: EP01967450A
Authority: EP
Inventors: François CANSELL
Original assignee: Centre National de la Recherche Scientifique CNRS
Current assignee: Innoveox
Priority date: 2000-09-07
Filing date: 2001-09-07
Publication date: 2003-06-18
Anticipated expiration: 2021-09-07
Also published as: WO2002020414A1; US20030189012A1; CN1452597A; CA2421167C; FR2813599B1; CN1244504C; KR100805923B1; FR2813599A1; EP1318968B1; JP2004508179A; JP4852222B2; KR20030029920A; PT1318968E; ES2529169T3; BR0113722B1; DK1318968T3; MXPA03001939A; US6929752B2; CY1115995T1; AU2001287829A1

Abstract

The invention concerns a method for oxidising organic matter contained in an aqueous effluent and an installation for implementing said method. Said method comprises the following steps: injecting into a tubular body said aqueous effluent; bringing said aqueous effluent to a pressure P1, corresponding to the critical pressure of said aqueous effluent; bringing said aqueous effluent to a temperature T1; and injecting into said tubular body at n points spaced apart from one another, n fractions of at least an oxidising composition, so that a portion of the thermal energy produced by the oxidation reaction increases the temperature of the reaction mixture from said temperature T1 to temperature T2 > T1 according to an increasing curve, whereby said organic matter is oxidised, said reaction mixture continuously developing from a sub-critical liquid state to the supercritical domain.

Description

Waste treatment process by hvdrothermal oxidation

The present invention relates to a hydrothermal oxidation process for waste, in particular but not exclusively to organic bodies contained in an aqueous effluent, and to an installation intended for the implementation of said process.

Applications of the invention are in particular, but not exclusively, the transformation of organic bodies contained in small quantities in aqueous effluents originating in particular from the agro-food industries. These aqueous effluents are also likely to contain dissolved salts. Organic bodies are transformed into gases capable of being burned to provide energy or gases capable of being released into the atmosphere without danger.

Methods for transforming organic waste contained in an aqueous phase are known. In particular, it is known to bring the water / organic waste mixture to temperatures and pressures such that the water exceeds its critical point thus causing, when an oxidizing body is present in the mixture, the decomposition of the waste into chemical elements. simple of the CO ₂ and H ₂ O type. However, when the water / organic waste mixture to which has been added quantities of oxidant capable of oxidizing all the waste is compressed and heated so that the water exceeds its critical point, the oxidation reaction which takes place produces significant amounts of thermal energy which can affect the integrity of the walls of the reactor in which the reaction takes place. The same consequences are observed on the walls of the reactor when the water / organic waste mixture is previously compressed and heated to the introduction of the oxidant into the mixture.

On the other hand, when the oxidant is introduced before having started to compress and heat the mixture, hot spots may appear within the reactor. These are due essentially the fact that the solubility of the oxidant and its heat capacity are not constant depending on the temperature and pressure conditions of the mixture. Thus, the concentration of oxidant dissolved in the mixture is not homogeneous in the reaction medium and the oxidation reaction produces a greater amount of thermal energy in the zones of greater concentration of oxidant.

In addition to the fact that the appearance of these hot spots is liable to affect the walls of the reactor, the poor distribution of the oxidant in the reaction medium leads to a poor yield of the reaction for degrading organic waste.

To remedy the localized heating of the reactor, it has been imagined to inject oxygen and water simultaneously in fractions along the reactor, so that the oxygen oxidizes the organic matter and that simultaneously, the water lowers the temperature of the reaction medium. However, this solution does not allow optimal degradation of the organic matter, since the oxidation rate is reduced by the simultaneous lowering of the temperature. In addition, the thermal profile of the reactor has an alternately increasing and then decreasing curve with each injection, which decreases the overall efficiency of the reactor.

A first object of the present invention is to provide a process for the oxidation of organic compounds contained in aqueous effluents which makes it possible to remedy the aforementioned drawbacks. This object is achieved, in accordance with the invention, because the method comprises the following steps:

- said aqueous effluent containing a determined quantity of organic bodies, taken under conditions of initial pressure and temperature, is injected into a tubular body having an inlet and an outlet. said aqueous effluent is brought to a pressure P1, corresponding at least to the critical pressure of said aqueous effluent, said pressure P1 being greater than the initial pressure,

- Said aqueous effluent is brought to a temperature T1 higher than the initial temperature by heating means applied in an area of said tubular body, and in that one injects into said tubular body at n points distant from each other, n fractions at least one oxidizing composition, the sum of which corresponds to the quantity of oxidizing composition necessary for the oxidation of said determined quantity of organic bodies, so that a portion of the thermal energy produced by the oxidation reaction increases the temperature of the reaction mixture from said temperature T1 to temperature T2> T1 according to an increasing curve between said zone of said tubular body and the ^th injection point, whereby said organic bodies are oxidized, said reaction mixture continuously evolving from a state under - liquid criticism in the super-critical domain.

Thus, a characteristic of the process for the oxidation of organic bodies lies in the gradual injection of the exclusively oxidizing composition, through the n injection points, into the reaction medium which flows into the tubular body. In this way, the oxidation of the organic bodies contained in the aqueous effluent is carried out gradually during the flow of the reaction mixture in the tubular body and the thermal energy produced by the oxidation reaction on each injection of oxidizing composition. is partially dissipated between injections, which avoids too intense production of energy which would damage the internal walls of the tubular body. And, there is no need to inject a body capable of simultaneously cooling the reaction medium during the reaction. Obviously, the oxidizing composition is capable of containing other compounds, but which have no specific action on the reaction medium.

A portion of the total thermal energy produced by the oxidation of all organic bodies is transferred to the reaction medium, the pressure P1 of which is greater than the critical pressure of the aqueous effluent, which allows it to progressively evolve from one under critical state in liquid phase up to the supercritical domain, without passing through the gas phase. When the reaction mixture is in the supercritical domain, the concept of phase disappears and the organic bodies which have not been oxidized between the injections of oxidizing composition, are in this domain.

Advantageously, the pressure P1 of said aqueous effluent is greater than 23 MPa and the temperature T1 of said effluent is between 370 and 520 ° K. In this range of temperature and pressure, the aqueous effluent containing the organic bodies is in a liquid phase under criticism where a part of these bodies is oxidized.

According to a particular embodiment of the invention, said portion of thermal energy produced by the oxidation reaction increases the temperature of said reaction mixture at a temperature T2 below 800 ° K. Thus, although the temperature of the reaction mixture is likely to be greater than 800 ° K after the n ^th injection point since the n ^th fraction of oxidizing composition reacts with the remaining organic bodies, this amount of energy doesn’t is not sufficient to degrade the inner wall of the tubular body. Thus, a substantial part of the organic bodies is oxidized before the reaction mixture reaches the temperature T2, and the last part which is oxidized by the last fraction of oxidizing composition being low, the temperature of the reaction mixture will be very slightly higher than T2. In addition, the heat capacity of water is maximum for a temperature between 650 ° K and 700 ° K, which allows absorption significant thermal energy released by the oxidation reaction in this temperature range that the reaction medium passes through. The walls of the reactor will be all the less affected.

According to another particular embodiment of the invention, three fractions of an oxidizing composition are injected into said tubular body at three points spaced from one another. The first fraction is injected when the temperature of the aqueous effluent has reached the temperature T1, the second fraction is injected so that the aqueous effluent reaches the temperature T2 and, when it has reached it, the third fraction is injected .

Advantageously, the first fraction of oxidizing composition is injected after said aqueous effluent has reached the temperature T1, so that the oxidation reaction of organic bodies does not start until downstream of said zone of said tubular body where said said are applied. heating means.

According to yet another particular embodiment of the invention, said tubular body has a plurality of portions including. the sections are of different sizes. This configuration makes it possible alternately to provide narrower portions of tubular body in which the oxidizing composition is injected and larger portions where the oxidation reaction takes place. Thus, the residence time of the reaction mixture in the larger portions is greater, which makes it possible to increase the reaction time and therefore its yield between each injection of oxidizing composition. According to an advantageous arrangement, part of the thermal energy produced by said oxidation is transferred to said aqueous effluent taken under the initial pressure and temperature conditions in order to bring it to said temperature T1. In this way, it is not necessary to provide additional heating means to bring said aqueous effluent from the initial temperature to the temperature T1, which improves the total energy balance of the process according to the invention. Only low intensity starting heating means are necessary.

Preferably, the oxidizing composition injected into the tubular body is oxygen, which makes it possible to transform the organic bodies at an advantageous cost. However, hydrogen peroxide can be used in certain particular situations where the supply costs are advantageous where, when the conditions for implementing the process require an oxidizing composition of greater solubility in water. According to a particularly advantageous arrangement, at least one of the fractions of oxidizing composition consists of an oxidizing composition of a different nature from that of the other fractions. Thus, for example, it is possible to benefit from the technological advantages of hydrogen peroxide in a first part of the reactor and from the economic advantages of oxygen in the second part.

According to a particularly advantageous embodiment, the method according to the invention further comprises the following steps: recovering said aqueous effluent and the salts which it contains at said outlet from said tubular body, reducing the pressure of said aqueous effluent from said pressure P1 at a pressure PO, between atmospheric pressure and said pressure P1 so as to relax said aqueous effluent to transform all the salts in the solid state and said aqueous effluent in the vapor state; the salts are recovered in the solid state; and, said aqueous effluent is recovered in the vapor state, whereby said aqueous effluent and the salts which it contains are physically separated

A second object of the present invention is to propose an installation intended for implementing the process for the oxidation of organic bodies contained in aqueous effluents. The installation includes: - means for injecting into a tubular body, having an inlet and an outlet, said aqueous effluent containing a determined quantity of organic bodies, taken under the initial pressure and temperature conditions, - means for bringing said aqueous effluent to a pressure P1 higher than the initial pressure,

- heating means, applied in an area of said tubular body, to bring said aqueous effluent to a temperature T1, higher than the initial temperature, and, - means for injecting into said tubular body, where said aqueous effluent is at least the pressure P1, at n points distant from each other, n fractions of an oxidizing composition, the sum of which corresponds to the quantity of oxidant necessary for the oxidation of said determined quantity of organic bodies, so that a portion of the thermal energy produced by the oxidation reaction increases the temperature of the reaction mixture from said temperature T1 to temperature T2> T1 according to an increasing curve between said zone of said tubular body and the n ^th injection point, whereby said organic bodies are oxidized, said reaction mixture continuously evolving from a state in subcritical phase to a state in supercritical phase.

Advantageously, the tubular body consists of a tube having an inlet orifice into which said aqueous effluent is injected and an outlet orifice through which said oxidized organic bodies escape. Said tube can be straight when the process can be implemented in a tubular body of short length, but it can also be arranged in a helix so as to reduce the total dimensions of the reactor.

Preferably, the means for injecting said aqueous effluent comprise a pump capable of compressing said aqueous effluent to a pressure greater than 23 MPa, said pump being connected to said inlet orifice. Thus, the pump which also includes an intake port aqueous effluent and a pressure injection port injects said aqueous effluent into the tubular body. The pressure of the effluent in the tubular body is relatively constant and greater than 23 MPa at least in the portion where the oxidation reactions take place. Advantageously, said heating means, applied in said zone of said tubular body comprise a thermoelectric generator integral with said tubular body. Thus, the thermoelectric generator fixed on the tubular body makes it possible to preheat the aqueous effluent which is injected. Preferably, said heating means, applied in said zone of said tubular body, comprise a heat exchanger integral with said tubular body, the hot source of which is supplied by part of the thermal energy produced by said oxidation reaction. In fact, the oxidation reaction produces thermal energy, at least a portion of which can increase the temperature of the reaction medium and a portion of which can be recovered and used to bring the aqueous effluent to temperature T1.

According to a particular embodiment of the invention, the means for injecting an oxidant fraction into said tubular body comprise a variable-flow injector opening into said tubular body, the oxidizing pressure in said injector being greater than P1. The injector can be supplied with an oxidizing composition by a pump capable of compressing the oxidizing composition to a pressure greater than P1, or by a reservoir containing the composition under a pressure also greater than P1.

According to a particular embodiment of the invention, the means for injecting the oxidant into said tubular body include three injectors opening into said tubular body, spaced from one another. Advantageously, the first injection point of the oxidizing composition is located between said outlet orifice of said tubular body and said area of said tubular body where said heating means are applied, near the latter.

According to a particular mode of implementation, the oxidation installation further comprises: means for recovering said aqueous effluent and the salts which it contains at said outlet from said tubular body., Means for reducing the pressure of said aqueous effluent from said pressure P1 to a pressure PO, between atmospheric pressure and said pressure P1 so as to relax said aqueous effluent to transform all the salts in the solid state and said aqueous effluent in the vapor state; means for recovering the salts in the solid state; and, means for recovering said aqueous effluent in the vapor state, whereby said aqueous effluent and the salts it contains are physically separated.

Other features and advantages of the invention will emerge on reading the description given below of particular embodiments of the invention, given by way of non-limiting indication, with reference to the appended drawings in which:

- Figure 1 is a schematic view of the installation for implementing the process according to the invention, comprising n injection point of the oxidizing composition, - Figure 2, is a view of the thermal profile of the reaction medium as a function of the injection points in oxidizing composition corresponding to the schematic view of FIG. 1,

FIG. 3 is a schematic view of the installation intended for implementing the method according to the invention according to a particular embodiment where the tubular body has three injection points, and,

- Figure 4 is a view of the thermal profile of the reaction medium as a function of the injection points corresponding to the schematic view of the installation shown in Figure 3. Reference will be made to FIG. 1 to describe the installation for implementing the process for the oxidation of organic bodies contained in the aqueous effluent.

The aqueous effluent containing the organic bodies to be transformed is stored upstream of the installation for implementing the process in a tank 10. The aqueous effluents are generally constituted by industrial or urban sludge, or by water resulting from industrial processes .

A pump 12, the inlet port 14 of which is connected by a pipe 16 to the lower end of the reservoir 10, is capable of pumping the aqueous effluent and of injecting it under pressure into a tubular body 18 at the level of its inlet orifice 20. The pump 12 is capable of injecting the aqueous effluent into the tubular body 18 under a pressure greater than 22 MPa which corresponds substantially to the critical pressure of the water.

The tubular body 18 is provided with a thermoelectric generator 22 which at least partially surrounds the external wall of the tubular body near the inlet orifice 20 into which the aqueous effluent is injected. The thermoelectric generator 22 consists of a heating resistor capable of producing enough thermal energy to raise the temperature of the aqueous effluent which passes through the tubular body 18.

It goes without saying that any other means capable of producing thermal energy can be used, in particular means operating on gas or other fuels. This energy supply to the aqueous effluent is necessary for the start of the oxidation reaction of organic bodies which takes place upon injection of a first fraction of oxidizing composition at the injection point 24. This injection point 24 is located in the tubular body 18 downstream of the thermoelectric generator 22. In a particular embodiment, the injection of the first fraction of oxidizing composition is carried out upstream of the heating means after the inlet of the tubular body so as to dissolve part of the oxidizing composition in the aqueous phase at the initial temperature.

At the injection point 24, an injector (not shown) passes through the wall of the tubular body 18 and opens into the lumen of the latter. The injector is connected to a pump 26 or to a reservoir (not shown) by means of a pipe 28. The pump 26 or the reservoir is capable of delivering a fraction of oxidizing composition under a pressure higher than the pressure of the effluent flowing from the tubular body 18. In fact, this condition is necessary for the oxidant to be injected into the tubular body 18;

The oxidizing composition can consist of any substance capable of removing electrons from organic bodies. The least expensive oxidant is oxygen and it is easy to inject using an injector. Other oxidants are likely to be used such as hydrogen peroxide or like nitric acid which has the advantage of degrading the nitrogen oxides and obtaining water and nitrogen.

A second injection point 30 of the oxidizing composition located near the first injection point 24, downstream, allows the injection of a second fraction of the oxidizing composition. The means used to inject the oxidizing composition are identical to the means. implemented to carry out the injection at the first point 24.

The number of fractions of oxidizing composition to be injected into the tubular body 18 is variable as a function of the concentration of organic bodies present in the aqueous effluent, of the quantity of oxidant necessary for the oxidation of all the organic bodies and according to of the geometry of the tubular body. A particular embodiment of the invention will be described in more detail in the following description, in which the installation comprises three injection points in an oxidizing composition.

According to an advantageous arrangement, when the temperature of the reaction medium is increased after the injection of the first oxidizing fraction, at least two types of oxidizing composition are used. The hydrogen peroxide is injected firstly given its strong oxidizing power and then oxygen fractions are injected at the other injection points. Once the reaction has started, the oxygen can react optimally. According to this mode of implementation, the economic balance of the reactor is improved because oxygen is less expensive than hydrogen peroxide.

According to Figure 1, the installation comprises a last point 32 of the oxidizing composition injection named n ^'th injection. In order for the oxidation reaction to be substantially complete, i.e. for all of the organic bodies to be oxidized, it is necessary that the quantity of oxidant injected into the aqueous effluent is at least equal to the quantities of oxidant corresponding to the stoichiometry of the oxidation reaction of organic bodies. Thus, the sum of the fractions of oxidizing composition injected into the tubular body 18 is at least equal to the amount of stoichiometric oxidant of the oxidation reaction of a given amount of aqueous effluent. Obviously, the oxidation process takes place continuously and the reasoning which is held for given quantities can be transposed to continuous operation by using flow measurements.

When the reaction is complete and the organic bodies contain only compounds based on carbon and oxygen, the oxidation products consist of carbon dioxide and water. These oxidation products are released at the end of the tubular body 18 at an outlet orifice 34.

The method according to the invention makes it possible to mineralize an organic charge contained in an aqueous effluent to obtain water and carbon dioxide, for example. In this case, the reaction products can perfectly be released into the atmosphere without damaging the environment, or recovered to be used as a reagent if the carbon dioxide content is sufficient. The products of the oxidation reaction of organic bodies can also be released into the atmosphere if, for example, they contain nitrogen resulting from the degradation of nitrogen oxides by nitric acid. On the other hand if the organic bodies contain chlorine, the hydrogen chloride coming from the reaction will have to be recovered by chemical transformation.

As will be described in more detail in the following description, the tubular body is a priori at its maximum temperature in the area located after the ^th injection point. Thus, it is possible to recover this thermal energy by means of a first exchanger 36 located in said zone where the temperature is maximum to transfer it upstream of the tubular body 18 by means of a second exchanger 38. This thermal energy transferred to proximity to the inlet orifice 20 of the tubular body 18 makes it possible to supplement or replace the thermoelectric generator necessary for preheating the aqueous effluent. This configuration is of economic interest by reducing the amount of energy necessary for the implementation of the method.

After having described the constituent elements of the installation necessary for the implementation of the process according to the invention with reference to Figure 1, we will now describe, with reference to Figure 2, the process for the oxidation of organic bodies present in the effluent and the thermal profile of the reaction medium. The latter is located directly above the device of FIG. 1 so that the thermal profile of the reaction medium corresponds to the different portions of the tubular reactor 18. The aqueous effluent is first compressed by means of the pump 12 before be injected under a pressure greater than 22 MPa into the inlet orifice 20 of the tubular body 18. The compression, which makes it possible to raise the temperature of the aqueous effluent, is supplemented by the second heat exchanger 38, if the installation is in normal operating mode or by the thermoelectric generator 22 if the installation is in transient mode. The reaction medium initially at the temperature Ti is thus brought to the temperature T1 along a slope 40 in accordance with the thermal profile of FIG. 2.

The temperature T1 is between 370 and 520 ° K while the pressure of the reaction medium is kept constant, which allows the reaction medium to be kept in the liquid phase. The latter maintains a constant temperature T1 during a transitional period corresponding to the plate 42.

Then, a first fraction of the oxidizing composition is injected at the first injection point 24 and the temperature of the reaction medium increases along the slope 44 to reach the temperature

T11. Indeed, the oxidation of organic bodies by the oxidizing composition is exothermic, and therefore gives up energy to the reaction medium.

A second fraction of the oxidizing composition is injected at the second injection point 30, producing energy capable of increasing the temperature to a value T12 along the slope 46.

The same operation is repeated as many times as necessary, taking care to control the temperature of the reaction medium by the controlled injection of the fractions of oxidizing composition. Before the injection of the ^nth fraction of oxidant into the tubular body 18 at the injection point 32, the temperature of the reaction medium must not be higher than the temperature T2 which is lower than 800 ° K.

In fact, in the contrary case, the risks of degradation of the internal wall of the tubular body 18 are significant, since the n ^th and last injection further increases the temperature of the reaction medium along a slope 48.

The last injection of oxidizing composition allows the degradation of the organic bodies of the aqueous effluents which have not been degraded during the preceding stages. In order to ensure maximum yield from the oxidation reaction, the sum of the n fractions of oxidizing composition is substantially greater than the amount stoichiometric required. Obviously, the process being continuous, it is the sum of the flows of the fraction of oxidizing composition relative to the flow of the aqueous effluent in the tubular body 18 which corresponds to an over-stoichiometric ratio. Furthermore, the heat capacity of water being maximum for a temperature substantially equal to 670 ° K, advantageously a large fraction of oxidizing composition is injected in a temperature range of the reaction medium comprising this value of 670 ° K. In fact, since the heat capacity of water is maximum at this temperature value, the thermal energy produced by the oxidation reaction is all the better absorbed, which limits the increase in the temperature of the reaction media. and therefore the degradation of the internal wall of the tubular body 18.

In addition, when the oxidizing composition is oxygen, it is soluble in the liquid phase of the aqueous effluent for all injections. This interesting feature makes it possible to avoid hot spots in the tubular body. Indeed, the total solubility of oxygen in the reaction medium allows a homogeneous and instantaneous distribution of the oxidant, which produces a thermal increase of the whole of the reaction medium since the reactions start substantially at the same instant. Conversely, poor solubility of the oxidant induces reactions localized within the reaction medium and therefore hot spots.

Reference will be made to FIGS. 3 and 4 to describe a particular embodiment comprising three injection points for three fractions of oxidizing composition.

Found in Figures 3 and 4 the installation according to the invention and the thermal profile associated with it. The aqueous effluent is injected under pressure through the inlet orifice 20. The preheating means as well as the injection of the first fraction of oxidizing composition at the injection point 24 allow the reaction medium reaching the temperature T1 during a transitional period corresponding to the plateau 50. The injection of the second fraction of oxidizing composition at the injection point 30 produces an increase in temperature to a value T2 corresponding to the plateau 52. Then, the last injection, which allows the oxidation of organic bodies which have not yet reacted, raises the temperature of the reaction medium to a temperature substantially above T2. Obviously, the values of T1 and T2 are here the same as the values T1 and T2 mentioned in Figures 1 and 2. According to another particular embodiment, not shown, retaining the principle described above according to which injects three oxidant fractions, the injection of the first fraction is carried out at an injection point located in the tubular body upstream of the preheating means near the inlet orifice of the tubular body. Thus, the oxidizing composition constitutes with the aqueous effluent containing the organic bodies a reaction medium whose temperature is substantially equal to the initial temperature of the aqueous effluent. The preheating means allow the oxidation reaction to start from the first temperature rise of the reaction medium which is itself produced by the reaction.

According to another embodiment, not shown, only two fractions of oxidizing composition are injected. This configuration is advantageous when the concentration of organic bodies in the aqueous effluent is low. A particular embodiment of the invention is given by way of indication in the description which follows.

The tubular body or reactor has four injection points and a preheater which allows the temperature of the aqueous effluent to be brought to a temperature of 425 ° K. The effluent to be treated consists of a mixture of glucose and methanol containing 3.9% by weight of glucose and 4.9% of methanol in an aqueous phase. To completely oxidize this mixture, the quantity of oxygen required is 88.9 g / l; This quantity is called "chemical oxygen demand" or, more usually, COD. The quantity injected here corresponds to a stoichiometry of 1, 1.

The flow rate of the effluent in the reactor is 1 kg / hour at a pressure of 25 MPa.

The table below represents the measurement of the length of the reactor in meters, the point 0 being substantially the point of injection of the aqueous effluent, the position of the injections of the oxygen fractions and the corresponding temperature of the reactor.

The above example is in no way limiting, and it would not go beyond the scope of the invention to treat any other composition of effluent with using a different oxidant and an installation comprising a different number of injection points.

According to another aspect, the oxidation installation comprises means, not shown, for recovering the salts contained in the aqueous effluents.

Thus, the tubular body is extended at its exit by a second tubular body in which the aqueous effluent and the salts which it contains pour out at a temperature between 750 and 900 ° K, for example 820 ° K. The second tubular body has an inlet nozzle into which water can be injected to cool the aqueous effluent to a temperature between 700 and 800 ° K, for example 750 ° K.

The second tubular body opens into a receptacle forming a hopper via an expansion nozzle. The internal pressure of the receptacle being between atmospheric pressure and said pressure P1, for example 1MPa. In this way, the aqueous effluent containing the salts relaxes, all the salts are transformed into a solid state, and the aqueous effluent in the vapor state. It is thus possible to recover the salts at the lower end of the hopper and the steam to another outlet provided for this purpose at a temperature between 500 and 600 ° K, for example 550 ° K.

In addition, in a particularly advantageous manner, the outlet from the tubular body and / or the second tubular body comprises an ultrasonic decolmator, applied to the external walls, making it possible to unclog the salts which settle on the internal wall of the tubular bodies and which are liable to clog during the oxidation process.

Claims

1. Process for the oxidation of organic bodies contained in an aqueous effluent, said aqueous effluent being capable of containing salts, characterized in that it comprises the following steps:

- Is injected into a tubular body (18) having an inlet and an outlet said. aqueous effluent containing a determined quantity of organic bodies, taken under conditions of initial pressure and temperature,

said aqueous effluent is brought to a pressure P1, corresponding at least to the critical pressure of said aqueous effluent, said pressure P1 being greater than the initial pressure,

- said aqueous effluent is brought to a temperature T1 higher than the initial temperature by heating means (38, 22) applied in an area of said tubular body, and in that one injects into said tubular body at n points (24, 30, 32) distant from each other, n fractions of at least one oxidizing composition, the sum of which corresponds to the quantity of oxidizing composition necessary for the oxidation of said determined quantity of organic bodies, so that a portion of the thermal energy produced by the oxidation reaction increases the temperature of the reaction mixture from said temperature T1 to temperature T2> T1 according to an increasing curve (44, 46) between said zone of said tubular body and the n ^th point of injection, whereby said organic bodies are oxidized, said reaction mixture continuously evolving from a liquid subcritical state to the supercritical domain.

2. Oxidation process according to claim 1 characterized in that said pressure P1 of said aqueous effluent is greater than 23 MPa and in that the temperature T1 of said effluent is between 370 and 520 ° K.

3. Oxidation process according to claim 1 or 2 characterized in that said portion of thermal energy produced by the oxidation reaction increases the temperature of said reaction mixture at a temperature T2 below 800 ° K.

4. Oxidation method according to any one of claims 1 to 3 characterized in that three fractions of an oxidizing composition are injected into said tubular body (18) at three points (24, 30, 32) spaced apart. each other.

•

5. An oxidation process according to any one of claims 1 to 4, characterized in that the first fraction of oxidizing composition is injected after said aqueous effluent has reached the temperature T1.

6. Oxidation method according to any one of claims 1 to 5 characterized in that said tubular body (18) has a plurality of portions whose sections are of different sizes.

7. An oxidation process according to any one of claims 1 to 6 characterized in that, in addition, part of the thermal energy produced by said oxidation is transferred to said aqueous effluent taken under the initial pressure and temperature conditions in order to to bring it to said temperature T1.

8. Oxidation method according to any one of claims 1 to 7 characterized in that the oxidizing composition is oxygen.

9. An oxidation process according to any one of claims 1 to 7 characterized in that the oxidizing composition is hydrogen peroxide.

10. Oxidation process according to any one of claims 1 to 7 characterized in that at least one of the fractions of oxidizing composition consists of an oxidizing composition of a different nature from that of the other fractions.

11. Oxidation process according to any one of claims 1 to 10, characterized in that it further comprises the following steps:

- said aqueous effluent and the salts it contains are recovered at said outlet from said tubular body,

the pressure of said aqueous effluent is lowered from said pressure P1 to a pressure PO, comprised between atmospheric pressure and said pressure P1 so as to relax said aqueous effluent to transform all the salts in the solid state and said aqueous effluent to vapor state; - The salts are recovered in the solid state; and,

- Said aqueous effluent is recovered in the vapor state, whereby said aqueous effluent and the salts it contains are physically separated.

12. Installation for oxidizing organic bodies contained in aqueous effluents, characterized in that it comprises: - means for injecting (12, 20), into a tubular body having an inlet and an outlet, said aqueous effluent containing a determined quantity of organic bodies, taken under the initial pressure and temperature conditions,

- means (12) for bringing said aqueous effluent to a pressure P1 greater than the initial pressure,

heating means (38, 22), applied in an area of said tubular body (18), to bring said aqueous effluent to a temperature T1, higher than the initial temperature, and,

means for injecting (26, 28) into said tubular body, where said aqueous effluent is at least at pressure P1, at n points (24, 30,

32) distant from each other, n fractions of an oxidizing composition, the sum of which corresponds to the quantity of oxidant necessary for the oxidation of said determined quantity of organic bodies, so that a portion of the thermal energy produced by the oxidation reaction increases the temperature of the reaction mixture from said temperature T1 to temperature T2> T1 according to an increasing curve between said zone of said tubular body and the n ^th injection point, whereby said organic bodies are oxidized, said reaction mixture continuously evolving from a state in subcritical phase to a state in supercritical phase.

13. Oxidation installation according to claim 12, characterized in that said tubular body (18) consists of a tube having an inlet orifice (20) into which is injected said aqueous effluent and an outlet orifice (34 ) through which said oxidized organic bodies escape.

14. Oxidation installation according to claim 12 or 13, characterized in that the means for injecting said aqueous effluent comprise a pump (12) capable of compressing said aqueous effluent to a pressure greater than 23 MPa, said pump being connected to said orifice inlet (20).

15. Oxidation installation according to any one of claims 12 to 14, characterized in that said heating means (38, 22), applied in said zone of said tubular body comprise a thermoelectric generator (22) integral with said tubular body.

16. Oxidation installation according to any one of claims 12 to 15, characterized in that said heating means (38, 22), applied in said zone of said tubular body (18), comprise a heat exchanger (38) integral said tubular body (18), the hot source of which is supplied by part of the thermal energy produced by said oxidation reaction.

17. Oxidation installation according to any one of claims 12 to 16, characterized in that the means for injecting (26, 28) a fraction of oxidant into said tubular body comprise a variable-flow injector opening into said tubular body (18), the pressure in oxidizing in said injector being greater than P1.

18. Oxidation installation according to any one of claims 12 to 17, characterized in that the means for injecting the oxidizer in said tubular body comprise at least two injectors opening into said tubular body, spaced from each other.

19. Oxidation installation according to any one of claims 12 to 18, characterized in that the first injection point (24) of the oxidizing composition is located between said outlet orifice (34) of said tubular body (18) and said zone of said tubular body where said heating means are applied, near the latter.

20. Oxidation installation according to any one of claims 12 to 19, characterized in that it further comprises: - means for recovering said aqueous effluent and the salts which it contains at said outlet from said tubular body,

means for lowering the pressure of said aqueous effluent from said pressure P1 to a pressure PO, comprised between atmospheric pressure and said pressure P1 so as to relax said aqueous effluent to transform all the salts in the solid state and said aqueous effluent to vapor state;

- Means for recovering the salts in the solid state; and,

- Means for recovering said aqueous effluent in the vapor state, whereby said aqueous effluent and the salts it contains are physically separated.